Patent Literature 1 describes a technology, in which, in a hydraulic control device, full hysteresis characteristics which represent hysteresis to hydraulic pressure change characteristics composed of pressurization characteristics and depressurization characteristics are provided as a reference map, and when minor loops, which are turned back at midway positions within a range of the hydraulic change characteristics, go on, a plurality of reduced maps, which are obtained by reducing the reference map in response to turning-back positions, are created for each of such minor loops from the past to the present point of time, and a hysteresis hydraulic pressure correction amount is arithmetically operated by a sum of respective hysteresis hydraulic correction amounts obtained by the plurality of reduced maps at the same indicated current position. In such a configuration, the hydraulic control can be performed in accordance with highly accurate hysteresis characteristics; however, there is a problem that an enormous calculation resource is required.
Patent Literature 2 describes a technology, in which, in a torque transmission system using a hydraulic clutch for controlling driving force distributed to front/rear wheels of a vehicle, hystereses at a pressurization time and a depressurization time are simply estimated by using a pressurization side hydraulic pressure—torque characteristic table and a depressurization side hydraulic pressure—torque characteristic table, and based on the estimated hystereses, a command hydraulic pressure is calculated in accordance with characteristics which differ between the pressurization time and the depressurization time. Here, which of the tables is to be used is decided by determining whether or not there is a request to fasten the clutch or a request to increase fastening force thereof (pressurization request) or a request to release the fastening or a request to reduce the fastening force based on the driving force (command torque) distributed to the front/rear wheels in response to a running state of the vehicle. Such a configuration can be made simple; however, switching of the hysteresis characteristics between the pressurization time and the depressurization time is performed only based on such required driving force (command torque), and accordingly, sufficient accuracy cannot be obtained.